Push broom clutter rejection using a multimodal filter

ABSTRACT

A ground imaging system for use on a guided aerobody includes one or more lenses designed to receive EM radiation from a ground level, a filter substrate having a plurality of filters, a sensor array designed to receive the EM radiation from the filter substrate, and a processing device coupled to the sensor array. The filter substrate is located at a focal plane of the one or more lenses such that the filter substrate receives the EM radiation from the one or more lenses. The plurality of filters includes at least polarization filters and multispectral filters. The processing device is designed to analyze multispectral and polarization signatures of the electromagnetic radiation from identified objects at the ground level and determine that one or more of the objects is not a desired target based at least on the hyperspectral and polarization signatures of the one or more objects.

BACKGROUND

Guidance systems for projectiles, such as precision guided munitions,are used in various applications, including targeting applications thatinvolve a specific target that is proximate one or more non-targets. Byefficiently and effectively determining correct targets fromnon-targets, the risk of collateral or otherwise unintended damage isminimalized or otherwise reduced. Since the guided projectile is movingquickly, the guidance system must also make decisions quickly regardingwhether an identified object within the system's field of view isfriend, foe, or natural (e.g., a rock or vegetation). Accordingly,improvements to how quickly such guidance systems can identify what anobject is can greatly increase successfully guiding to an intendedtarget. There are many complex challenges regarding how to efficientlyanalyze received imaging data from a surrounding area to quicklyidentify a desired target from amongst other possible targets.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of embodiments of the claimed subject matterwill become apparent as the following Detailed Description proceeds, andupon reference to the Drawings, in which:

FIG. 1A illustrates a guided projectile imaging a portion of the groundthat is mapped across a filter substrate, in accordance with someembodiments of the present disclosure.

FIG. 1B illustrates a top-down view of the filter substrate used on theguided projectile from FIG. 1A, in accordance with some embodiments ofthe present disclosure.

FIG. 2 illustrates an example ground imaging system coupled to aguidance system for use onboard a guided areobody, according to someembodiments of the present disclosure.

FIG. 3 illustrates a top-down view of an example filter substrate havingcolumns of different filters, in accordance with some embodiments of thepresent disclosure.

FIG. 4 illustrates a side view of an example filter substrate, inaccordance with some embodiments of the present disclosure.

FIG. 5 illustrates a guided projectile angled further towards the groundand a filter substrate designed to be moved to use different filters onportions of the received electromagnetic radiation, in accordance withan embodiment of the present disclosure.

FIG. 6 illustrates another example of a filter substrate, in accordancewith some embodiments of the present disclosure.

FIG. 7 illustrates a flowchart of a method of verifying target objectsusing output from filters of a filter substrate, in accordance with anembodiment of the present disclosure.

Although the following Detailed Description will proceed with referencebeing made to illustrative embodiments, many alternatives,modifications, and variations thereof will be apparent in light of thisdisclosure.

DETAILED DESCRIPTION

Techniques are disclosed for guiding projectiles to a designated targetor targets. In an embodiment, the guided projectile includes a groundimaging system that captures electromagnetic (EM) radiation from an areaof the ground in front of the projectile as it flies through the air. Asensor array, such as a focal plane array or a microbolometer of theimaging system, is designed to capture at least infrared radiation fromthe ground. Objects can be identified based on various signatures fromthe received infrared radiation. However, as previously noted,determining that a given object is the intended target of the guidedprojectile is challenging, especially when the identified object is atthe far end of the projectile's field of view (FOV). For example, anobject may be identified that is 6 Km away and has a sensor pixel sizeof 2×2 pixels. It is difficult to determine whether the object is anenemy tank, a large rock, a small building, a dense area of vegetation,etc. This is especially true for systems that only use one imagingmodality when analyzing the incoming EM radiation (e.g., systems thatonly use contrast difference to determine object location and type). Dueto the push-broom effect, as the guided projectile continues to flyforward, the object that was at 6 Km away becomes closer (e.g., at 4 Kmaway) and becomes larger in the FOV, thus encompassing more pixels ofthe sensor array (e.g., 3×3 pixels). A more accurate determination ofthe object type can be made based on receiving more image data about theobject (now 3×3 imaging pixels), however, some situations may result infailure if it takes too long to determine that the object is theintended target of the guided projectile. For example, in somesituations, by the time the projectile is able to determine that thetarget it was tracking is not an enemy vehicle, it may be too late tochange the course of the projectile.

Thus, and in accordance with some such embodiments, the ground imagingsystem further includes a filter substrate having a plurality ofdifferent types of filters in order to analyze a plurality of imagingmodalities of the ground around the projectile. Rather than projectingthe received EM radiation directly onto a sensor array, the received EMradiation is instead focused onto the filter substrate and then imagedonto a sensor array after passing through the filter substrate. Thefilter substrate includes a plurality of different filter types such aspolarization filters and multispectral filters to provide differentimaging modalities to be analyzed by a processing device. In particular,the filter substrate includes various columns or bands of differentfilter types such that EM radiation from a given object within thesystem's FOV will pass through multiple filter bands as the projectileflies closer to that object due to the push broom effect where sensorsare arranged in columns perpendicular to the direction of travel inorder to collect data along different columns of sensors as theprojectile moves towards the object. According to some embodiments, theprocessing device is configured to analyze contrast, polarization, andmultispectral signatures of the EM radiation received via the filtersubstrate. These additional signatures yield more robust informationregarding the type of object being identified and allow for theprocessing device to quickly reject certain identified objects (alsoknown as clutter) as not being the intended target based on theircontrast, polarization, and/or multispectral signatures. According tosome embodiments, a field programmable gate array (FPGA) is used as theprocessing device due to its compact size and comparatively fastprocessing speed for its size.

According to some embodiments, contrast information from the received EMradiation is analyzed first to determine the presence of objects,followed by analysis of polarization and/or multispectral signatures ofthe identified objects to determine the type of object. For example, aman-made vehicle, such as a tank, typically has numerous flat surfacesthat produce a particular polarization signature, but a naturallyoccurring object, such as a rock, typically has numerous rough surfacesthat would produce a very different polarization signature.Multispectral signatures can also be used to determinewavelength-specific intensities from certain objects that can be used toidentify what those objects are.

The techniques may be embodied in devices, systems, methods, ormachine-readable mediums, as will be appreciated. For example, accordingto one example embodiment of the present disclosure, a ground imagingsystem for use on a guided aerobody includes one or more lenses designedto receive EM radiation from objects and terrain at a ground level, afilter substrate having a plurality of filters, a sensor array designedto receive the EM radiation from the filter substrate, and a processingdevice coupled to the sensor array. The filter substrate is located at afocal plane of the one or more lenses such that the filter substratereceives the EM radiation from the one or more lenses. The plurality offilters includes at least polarization filters and multispectralfilters. The processing device is designed to analyze multispectral andpolarization signatures of the electromagnetic radiation from theobjects and terrain at the ground level, and determine that one or moreof the objects is not a desired target based at least on thehyperspectral and polarization signatures of the one or more objects.

According to another example embodiment, a filter substrate for use inan imaging system includes a substrate that includes a plurality ofpolarization filters arranged in first columns, a plurality ofmultispectral filters arranged in second columns, and a plurality ofunfiltered regions arranged in third columns. The filter substrate isdesigned to receive electromagnetic radiation and map theelectromagnetic radiation onto a sensor array. The first columns, secondcolumns, and third columns are adjacently arranged one after the other.

Numerous examples are described herein, and many others will beappreciated in light of this disclosure.

General Overview

FIG. 1A illustrates a guided areobody 102 in flight over a groundsurface 104. Guided aerobody 102 may be any long- or short-rangeprojectile such as a missile or rocket with guidance capability toaffect its trajectory mid-flight. In one embodiment, the guidance systemonboard aerobody 102 includes a guidance component that controls aflightpath of areobody 102 and an imaging component that receives EMradiation received from an area around areobody 102 or from a portion ofground surface 104 beneath areobody 102. The imaging component ofaerobody 102 has a field of view (FOV) 106 across a portion of groundsurface 104. In the illustrated example, FOV 106 extends between about 2Km and about 6 Km from the front of areobody 102. These numbers areprovided as just one example, and the exact extent of FOV 106 isdependent both on the optics of the imaging system itself and thealtitude of areobody 102 above ground surface 104.

EM radiation is received from objects within FOV 106. These objects mayinclude any type of large structure, vehicle, or naturally occurringthing, such as tanks, boats, trucks, man-made structures, rocks, terrainformations, vegetation, etc. One of the detected objects may be anintended target of areobody 102. Thus, the imaging system and guidancesystem work together to identify the intended target from amongst thevarious detected objects and steer areobody 102 towards the intendedtarget. According to some embodiments discussed herein, varioussignatures from the EM radiation received from the objects (such aspolarization, contrast, and multispectral signatures) are used toquickly filter out objects that are not the intended target.

FIG. 1B illustrates a filter substrate 108 that is part of imagingcomponent onboard areobody 102, according to some embodiments. The EMradiation received across FOV 106 along ground surface 104 is projectedonto filter substrate 108. Filter substrate 108 includes a plurality ofdifferent filter types across its surface in order to analyze differentspectral or polarization signatures of the received EM radiation. Forexample, filter substrate 108 includes a plurality of polarizationfilters for filtering different polarization angles and a plurality ofmultispectral filters to provide different wavelength signatures. Insome embodiments, filter substrate 108 also includes regions where nofilters are provided (e.g., the EM radiation passes through filtersubstrate 108 with little to no modulation). The un-modulated EMradiation may be used for contrast analysis to determine locations ofobjects within FOV 106.

Objects that are imaged at the far end of FOV 106 (e.g., at 6 Km away)will continue to be imaged as areobody 102 moves closer to them. Objectsalso will get larger as areobody 102 moves closer to them. In otherwords, an object first imaged at 6 Km will also be imaged at a closerlocation, such as at 4 Km, (and look larger), and again will be imagedat an even closer location, such as 3 Km, (and look even larger). Asobjects become larger within FOV 106, more EM radiation can be collectedfrom the objects and more information can be analyzed about them. Bymapping the EM radiation collected from FOV 106 across filter substrate108, EM radiation collected from a given object on ground surface 104 iseffectively scanned across filter substrate 108 in the direction ofarrow 111 due to the push broom effect. For example, an object imaged at6 Km away will have its EM radiation received at first region 110 offilter substrate 108. When the object is 4 Km away, it will have its EMradiation received at second region 112 of filter substrate 108. Whenthe object is 3 Km away, it will have its EM radiation received at thirdregion 114 of filter substrate 108. And when the object is 2 Km away, itwill have its EM radiation received at fourth region 116 of filtersubstrate 108. Accordingly, filter structures on a surface of filtersubstrate 108 are arranged in columns (or rows depending on one'sperspective) within various sections of filter substrate 108 thatcorrespond to distance away from areobody 102, according to someembodiments. In one example, each of first region 110, second region112, third region 114, and fourth region 116 includes columns ofpolarization filters, multispectral filters, and contrast regions (e.g.,no filtering). According to some embodiments, first region 110 includesa fewest number of columns compared to the other regions because objectswill be smallest at the furthest distance away in FOV 106, and fourthregion 116 includes the most columns compared to the other regionsbecause objects will be largest at the closest distance within FOV 106.According to some embodiments, any given column on filter substrate 108includes one type of filter (e.g., polarization, multispectral, orcontrast). Further details regarding the arrangement of the differentfilters on filter substrate 108 are described with reference to FIGS. 3and 4.

FIG. 2 illustrates an example ground imaging system 201 coupled to aguidance system 212 for use onboard a guided areobody, according to someembodiments. Ground imaging system 201 includes a lens 202, a filtersubstrate 204, a sensor array 206, and a processing device 208. EMradiation is received from across the FOV in front of the areobody andcollected at lens 202 where it is focused onto filter substrate 204.According to some embodiments, filter substrate 204 is placed at thefocal plane of lens 202. Filter substrate 204 may have an arrangement offilters across its surface in accordance with any of the examplesdiscussed herein.

Lens 202 may represent any number of lenses or other passive opticalcomponents designed to focus the received EM radiation onto filtersubstrate 204. After the light passes through filter substrate 204, itis imaged across a two-dimensional sensor array 206. The various columnsof sensors of sensor array 206 correspond to columns of filters onfilter substrate 204, according to some embodiments. Accordingly, somecolumns of sensors of sensor array 206 receive polarized light whileother columns of sensors of sensor array 206 receive multispectral bandsof the received EM radiation. Still other columns of sensors of sensorarray 206 receive unfiltered light, according to an embodiment. Sensorarray 206 may be a microbolometer or a focal plane array. According tosome embodiments, the sensors of sensor array 206 are designed to beparticularly sensitive to light within the long wave infrared (LWIR)portion of the EM spectrum.

Each sensor of sensor array 206 may be referred to as a single pixel. Agiven object has a certain pixel size depending on its distance away,which grows larger as the object gets closer. For example, an objectsaid to have a pixel size of 2×2 at a distance of 6 Km away means thatthe EM radiation from the object is received across a 2×2 portion ofsensors in sensor array 206. As the object gets closer, a larger numberof sensors (e.g., 4×4 pixels) will receive EM radiation from the object.Additionally, because columns of sensors of sensor array 206 correspondwith columns of filters on filter substrate 204, EM radiation receivedfrom a given object is scanned across the sensors of sensor array 206 inthe same way that it is received across filter substrate 204 due to thepush broom effect. Accordingly, certain columns of sensors may bedesignated to receive different signatures of the received EM radiationbased on the filters (or no filters) the EM radiation passed through asit traversed through filter substrate 204.

The output of sensor array 206 is received by a processing device 208.Generally, As used herein, the term “processing device” may refer to anydevice or portion of a device that processes electronic data fromregisters and/or memory to transform that electronic data into otherelectronic data that may be stored in registers and/or memory. Accordingto some embodiments, processing device 208 comprises afield-programmable gate array (FPGA) architecture due to its speed inanalyzing multiple sensor inputs at once and due to its relatively smallcircuit board footprint for its processing power. Processing device 208may use image processing techniques to analyze the input received fromthe various pixels of sensor array 206 to determine locations ofobjects. According to some embodiments, determination of an object'sexistence is made via contrast determination with the raw, unfiltered EMradiation. That is, certain columns of pixels of sensor array 206receive unfiltered light, and the output of these sensors can be used todetermine contrast differences of the received light to make out whetheran object is present. The size of the object corresponds to the numberof pixels and the location of the pixels on sensor array 206 thatcorrespond to EM radiation received from the object. For example, afirst object identified in a 2×2 cluster of pixels at one end of sensorarray 206 corresponds to the first object having a first size at a firstdistance away, while a second object identified in a 2×2 cluster ofpixels at the opposite end of sensor array 206 corresponds to a secondobject that is smaller than the first object and is closer than thefirst object. For the sake of comparison, if the first object was closer(e.g., imaged using the pixels at the opposite end of sensor array 206,it would be identified in a greater number of pixels (e.g., 6×6 pixels).

According to some embodiments, processing device 208 is coupled to anobject database 210. Object database 210 includes one or more memorydevices such as volatile memory (e.g., dynamic random-access memory(DRAM)), nonvolatile memory (e.g., read-only memory (ROM)), flashmemory, solid state memory, and/or a hard drive. According to someembodiments, object database 210 stores known sizes for a variety ofpossible objects in order to help eliminate identified objects frombeing the desired target. Object database 210 may store objects ashaving a certain known size which corresponds to a given number ofpixels on sensor array 206 at a given distance away. For example, a tankmay be stored in object database 210 as having a certain size thatcorresponds to a 2×2 cluster of pixels when the tank is 6 Km away, or a4×4 cluster of pixels when the tank is 3 Km away. Any number of possibleobjects and their associated size can be stored in object database. Insome embodiments, further distinguishing features or details are storedabout a given objects, such as known multispectral or polarizationsignatures of a given object that can be used to positively identify theobject based on the polarized and multispectral EM radiation received atsensor array 206.

According to some embodiments, processing device 208 uses knowninformation about the desired target from object database 210 toeliminate identified objects that are not the desired target. Forexample, if a desired target is known to have a size corresponding to2×2 pixels at a distance of 6 Km, then any objects identified from thesensors that correspond to EM radiation received from 6 Km away can beeliminated if they are found to be smaller than 2×2 pixels or largerthan 2×2 pixels. In this example, further analysis is performed on allobjects that are 2×2 pixels (or close enough) to determine if any of theobjects is the desired target.

Once a first elimination of objects has been performed based on contrastdata, further analysis is performed on the remaining objects based onthe polarization and multispectral data, according to some embodiments.Recall that different columns of sensors on sensor array 206 can receiveEM radiation that has been filtered or polarized. The EM radiationreceived from any given object passes through multiple different filtertypes across filter substrate 204 as areobody 102 flies towards it.Either or both polarization and multispectral signatures may be used todistinguish between a desired target (e.g., a tank) and an undesiredtarget (e.g., a rock, vegetation, or structure having the same generalsize as the tank). Accordingly, further rounds of target elimination maybe performed using polarization and/or multispectral signatures to weedout other objects as not being the desired target. By eliminatingobjects as being the desired target, only the desired target will remain(assuming it is present in FOV 106).

According to some embodiments, processing device 208 is coupled to aguidance system 212 that controls the flightpath of areobody 102. Onceprocessing device 208 either positively identifies the target object oreliminates all possible objects except for the target object, processingdevice 208 sends the location of the desired object to guidance system212. Guidance system 212 may control any flight aspects of areobody 102(thrust, yaw, pitch, etc.) to change the flight trajectory. Once alocation of the desired target is known, guidance system 212 may alterthe flight path of areobody 102 to guide it to the desired target. Insome embodiments, guidance system 212 also has access to object database210 to further confirm any information regarding the desired target.

In some embodiments, guidance system 212 receives further input from aninertial navigation system (INS) located on areobody 102. In someembodiments, guidance system 212 obtains GPS data for some portion ofthe flight that can be used to identify position and tracking. Accordingto some embodiments, guidance system 212 uses the input from the INS andthe determined location of the desired target from processing device 208to affect an azimuth angle and/or an elevation angle of areobody 102 toensure that areobody 102 remains on course to intercept the intendedtarget. As noted above, one or more of the operations of guidance system212 may also be carried out by processing device 208.

It should be understood that ground imaging system 201 may include morecomponents or fewer components than the illustrated components withoutdeviating from its desired purpose of providing different forms offiltered EM radiation to sensor array 206. In some examples, guidancesystem 212 and processing device 208 are part of the same FPGA unit. Insome examples object database 210 is included within ground imagingsystem 201. According to some embodiments, ground imaging system 201 ismodular in design and can be installed or retrofitted to any areobodyhaving guidance capabilities.

FIG. 3 illustrates a top-down view of filter substrate 204, according tosome embodiments. As discussed previously, filter substrate 204 includesa plurality of different filter types that may be arranged in columnsacross filter substrate 204, where each column is configured with onefilter type. According to some embodiments, the columns of differentfilter types are grouped in different regions of filter substrate 204.For example, filter substrate 204 may include four different regions302-308 that correspond to EM radiation received at different distanceswithin the FOV of the areobody.

Each of regions 302-308 include columns of different types of filters.For example, a first region 302 includes column(s) of contrast filters302-1, column(s) of polarization filters 302-2, and column(s) ofmultispectral filters 302-3. A second region 304 includes column(s) ofcontrast filters 304-1, column(s) of polarization filters 304-2, andcolumn(s) of multispectral filters 304-3. A third region 306 includescolumn(s) of contrast filters 306-1, column(s) of polarization filters306-2, and column(s) of multispectral filters 306-3. And a fourth region308 includes column(s) of contrast filters 308-1, column(s) ofpolarization filters 308-2, and column(s) of multispectral filters308-3. It should be noted that for the purpose of this discussion, thecontrast filters represent regions of filter substrate 204 where nofiltering is occurring to the received EM radiation (e.g., receivedradiation is merely passed through with little to no modulation).Rather, the light received from these contrast regions is used toperform contrast detection and spatial filtering in software (e.g.,image processing software) to identify presence of objects.

For any given column(s) of filters, different filters may be present fordifferent wavelengths or polarization angles. For example, column(s) ofpolarization filters 302-2 include a first column of polarizationfilters for light having a 30-degree rotation at a first IR wavelengthband and a second adjacent column of polarization filters for lighthaving a 60-degree rotation at the first IR wavelength band or at adifferent IR wavelength band. According to some embodiments, each filterregion 302-308 includes columns of polarization filters across 6-10different angle rotations and across 3-5 different IR bands. In anotherexample, column(s) of multispectral filters 302-3 include a first columnof multispectral filters for a first IR wavelength band and at least asecond column of multispectral filters for a different IR wavelengthband. Any number of columns of multispectral filters can be provided toyield different IR wavelengths bands. In some embodiments, each filterregion 302-308 includes columns of multispectral filters across 4-10different IR wavelength bands.

According to some embodiments, a different number of total columns offilters are present within each of regions 302-308. This corresponds tothe expected size of imaged objects within the FOV (e.g., objects at thefar end of the FOV, corresponding to first region 302, are smaller thanobjects at the near end of the FOV, corresponding to fourth region 308).Thus, and in accordance with some embodiments, first region 302 includesthe fewest total number of columns of filters and fourth region 304includes the highest total number of columns of filters. In one example,first region 302 includes around 50 columns of filters (e.g.,corresponding to 50 columns of pixels on sensor array 206), secondregion 304 includes around 75 columns of filters (e.g., corresponding to75 columns of pixels on sensor array 206), third region 306 includesaround 100 columns of filters (e.g., corresponding to 100 columns ofpixels on sensor array 206), and fourth region 308 includes around 150columns of filters (e.g., corresponding to 150 columns of pixels onsensor array 206). In one particular example, first region 302 includes10 columns of contrast filters 302-1, 20 columns of polarization filters302-2, and 20 columns of multispectral filters 302-3.

According to some embodiments, filter substrate 204 includes unusedregions 310 between each of regions 302-308. Unused regions 310correspond to columns of sensors of sensor array 206 that areunprocessed to reduce the burden on processing device 208. Fewer ornarrower unused regions 310 will yield more imaging data to be analyzed,which may be possible if provided the requisite processing power.

FIG. 4 illustrates a side view of filter substrate 204, according tosome embodiments. The side-view shows each filter region 302-308 havingcolumn(s) of different filter types as well as contrast filters (shownoutlined with a dotted line). Filter substrate 204 includes a substrate402 that comprises a material providing little to no absorption of thereceived EM radiation of interest (e.g., generally radiation in theshort-wave IR range). In some examples, substrate 402 is borosilicateglass.

According to some embodiments, each of the columns of polarizationfilters, such as column(s) of polarization filters 308-3, are formedusing micro-sized grating structures that are lithographically patternedonto a surface of substrate 402. The spacing between the gratingpatterns and relative size of the grating lines dictates thepolarization angle of light that is allowed through. In someembodiments, the gratings are formed from metal or dielectric materials.The patterned grating structures are one example of thin film linearpolarizers.

According to some embodiments, each of the columns of multispectralfilters, such as column(s) of multi spectral filters 308-2, are formedfrom multiple layers of dielectric materials stacked on top of oneanother. The stacked dielectric layers can be very thin (on the order ofnanometers thick) and absorb or reflect specific wavelengths of light tocreate a notch filter. An arrangement of these notch filters is used tofilter the incoming EM radiation and create specific multispectralsignatures to be analyzed.

FIG. 5 illustrates a situation where areobody 102 has pitched itselfforward towards ground 104 such that it has a narrower FOV 502 of ground104. This situation may arise when a desired target has been identifiedand areobody 102 is angling downward to intercept the target. However,with FOV 502, the push-broom effect no longer occurs as the forwardmotion vector of areobody 102 along ground 104 is too small for objectsto be scanned across the various filter columns of filter substrate 204.Thus, as the guided projectile angles further towards the ground, thefilter substrate 204 can be moved to use different filters on portionsof the received electromagnetic radiation, in accordance with anembodiment of the present disclosure

In more detail, and according to some such embodiments, filter substrate204 is moved in order to pass the various filters across differentportions of EM radiation received across FOV 502. As can be seen, themovement may be a linear translation 504 or a circular motion 506. Notethat the circular motion 506 does not require any rotation of filtersubstrate 204 but rather circular movement within the XY plane. Thelinear translation 504 is in the X-direction to ensure that the EMradiation from across FOV 502 crosses over the different columns offilters on filter substrate 204. Any type of linear actuator may be usedto cause movement of filter substrate 204. In some embodiments, themotion of filter substrate 204 is timed with a frame rate of the camerathat includes sensor array 206. In one example, circular motion 506 isperformed to provide 0.001 inch by 0.001 inch motion for a desiredtarget having a pixel size of 2×2. In another example, lineartranslation 504 translates filter substrate 204 back and forth by 0.002inches each direction.

Different filters may be clustered together to ensure that multiplefilters interact with EM radiation received from a given object. Forexample, filter set 508 illustrates a mosaic of filters from columns ofpolarization filters on filter substrate 204. The 2×2 filter set 508includes four filters that correspond with 4 pixels (2×2 pixels) ofsensor array 206. Each of the polarization filters is designed to passthrough a different polarization angle of the light. According to someembodiments, circular motion 506 is applied to filter substrate 204 tomove each of the various filters in filter set 508 in the same circularmotion and ensure that the received EM radiation from a given object ispassed through each of the filters of filter set 508. This same conceptmay be applied to any sized filter set and across other types of filteras well, such as any of the multispectral filters.

FIG. 6 illustrates another example of a filter substrate 600, accordingto some embodiments of the disclosure. As can be seen, filter substrate600 is configured with a different design than filter substrate 204.Note, however, that filter substrate 600 can be used within groundimaging system 201 in the same way as filter substrate 204. According tosome embodiments, filter substrate 600 includes filter regions 602-608that each include roughly the same number of columns of filters. Forexample, each of filter regions 602-608 includes columns of polarizationfilters, multispectral filters and contrast filters that total around 50columns. According to some embodiments, a large central portion offilter substrate 600 includes a contrast region 610 that is used forcontrast determination of objects directly in front of the areobody,such as the situation illustrated in FIG. 5 where the areobody isfocusing in on its desired target and pitching downwards towards theground. Corresponding columns of sensors within the central portion ofsensor array 206 receive the light passing through contrast region 610.This received light may be used for final contrast determination of theobjects around the desired target to make any last second adjustments tothe flightpath of the areobody.

Methodology

FIG. 7 is a flowchart illustrating an example method 700 for identifyinga target object based on contrast, polarization, and multispectralsignatures of received EM radiation, in accordance with certainembodiments of the present disclosure. As can be seen, the examplemethod includes a number of phases and sub-processes, the sequence ofwhich may vary from one embodiment to another. However, when consideredin the aggregate, these phases and sub-processes form a process fortarget object identification and/or elimination of other objects frombeing the target object in accordance with certain of the embodimentsdisclosed herein. These embodiments can be implemented, for exampleusing the ground imaging system 201 in FIG. 2 as described above. Morespecifically, these embodiments can be implanted using processing device208. However other system architectures can be used in otherembodiments, as will be apparent in light of this disclosure. To thisend, the correlation of the various functions shown in FIG. 7 to thespecific components illustrated in the other figures is not intended toimply any structural and/or use limitations. Rather, other embodimentsmay include, for example, varying degrees of integration whereinmultiple functionalities are effectively performed by one system. Forexample, in an alternative embodiment a single module having decoupledsub-modules can be used to perform all of the functions of method 700.Thus, other embodiments may have fewer or more modules and/orsub-modules depending on the granularity of implementation. In stillother embodiments, the methodology depicted can be implemented as acomputer program product including one or more non-transitorymachine-readable mediums that when executed by one or more processorscause the methodology to be carried out. Numerous variations andalternative configurations will be apparent in light of this disclosure.

Method 700 begins at block 702 where the expected size of a desiredtarget is identified. Target size information may be stored in adatabase for a variety of different objects. The database can be updatedwith new objects or edited to change expected size parameters for any ofthe stored objects. The size information may be stored in associationwith a distance away from the areobody. For example, the size of tankmay be stored in the database as encompassing 2×2 pixels (e.g., of asensor array) at a distance of 6 Km, and 4×4 pixels at a distance of 3Km. The relative size of an object based on number of pixels on thesensor array is also dependent on the optics of the ground imagingsystem that receives the EM radiation. In some embodiments, otherdistinguishing features of the target object are provided in thedatabase, such as a shape of the target object or certain expectedmultispectral or polarization signatures of the target object.

Method 700 continues with block 704 where objects are identified usingcontrast determination from EM radiation received through contrastfilters (e.g., regions). According to some embodiments, certain columnarregions of a filter substrate allow light to pass through unfiltered sothat the raw EM radiation can be received and analyzed using imageprocessing techniques to identify contrast differences corresponding tolight reflecting off of different objects. Different sized objects maybe identified at a given distance away. The object distance correspondsto which pixels of the sensor array are being used to identify thepresence of the object, as discussed above. Since the target object sizefor the given distance is known, any other identified objects at thegiven distance that are either smaller or larger than the expected sizeof the target object can be eliminated as being the target object.Accordingly, only objects that are the same relative size as the targetobject are left for further analysis. According to some embodiments, theprocessing device may utilize a boost filter or other similar boosttechniques to sharpen edges of the contrast from the received EMradiation.

According to one example, the first 10 columns of sensors of a sensorarray are designated for contrast filtering and receive light from agiven distance away. The size of a desired target object is known to be2×2 pixels at the given distance away. Thus, using contrast filtering onthe received EM radiation across the first 10 or fewer columns ofsensors, any objects having a size of about 2×2 pixels are flagged aspossibly being the desired target object, any objects that are close insize (e.g., 1×1 or 3×3) are flagged as being less likely to be thedesired object, and any objects over a threshold size (e.g., 4×4 orgreater) are tossed out as not being the desired target object.According to some embodiments, objects flagged as being “less likely”may still be analyzed in future operations that involve multispectral orpolarization signatures. In some embodiments, objects flagged as being“less likely” undergo further contrast analysis either using input frommore sensors corresponding to the object's given distance away or fromsensors that correspond to the object being at a closer distance away ata later moment in time.

Method 700 continues with block 706 where the probable objects based onsimilar size to the desired target object are further analyzed todetermine what the objects are (e.g., rocks, vegetation, vehicular,building, etc.) According to some embodiments, this determination isperformed based on multispectral and/or polarization signatures from EMradiation received from the objects. As discussed above, the EMradiation received from the objects passes through columns ofpolarization and multispectral filters (as the areobody flies forward)to be received by corresponding columns of sensors in the sensor array.

With regards to the multispectral filters, they may be arranged incolumns of similar notch filters, or in a mosaic pattern (e.g., 2×2pixel cluster of four different notch filters for different stop bands).For a desired target object having a known size of N×N, certain ratiosof the received EM radiation from each of the N×N sensor pixels areanalyzed and compared to generate flags for the object as either beinglikely, less likely, or naturally occurring (e.g., a rock orvegetation).

With regards to the polarization filters, they may be similarly arrangedin columns of similar angle polarizations, or in a mosaic pattern (e.g.,2×2 pixel cluster of 4 different polarization angle filters). Accordingto some embodiments, polarized light is received having a differentpolarization angle from each column of polarization filters. The columnsof filters may be organized in pairs of opposing angles such thatadjacent polarization filter columns provide horizontal and verticalpolarization, or 30-degree rotation and 60-degree rotation to name a fewexamples. Certain ratios of the output from the pairs of polarizationfilter columns are analyzed to determine one or more polarizationsignatures of the object and can be used to determine if the object iseither likely, less likely, or naturally occurring (e.g., a rock orvegetation).

Following either or both the multispectral and polarization analysis,any objects determined to be naturally occurring can be eliminated asbeing the target object, according to some embodiments. In some cases,objects that are flagged as less likely following either or both themultispectral and polarization analysis are also eliminated, or theobjects undergo further multispectral and/or polarization analysiseither using input from more sensors corresponding to the object's givendistance away or from sensors that correspond to the object being at acloser distance away at a later moment in time.

Method 700 continues with block 708 where any objects not matchingexpected size or signature parameters of the target object areeliminated from being the desired target object. As noted above, thisblock may be performed as a part of block 704 and/or block 706.According to some embodiments, the goal of block 708 is to continuallyremove identified objects as being the desired target object as moreinformation is received from each of the different types of sensors(e.g., contrast, multispectral, and polarization) and from sensorscorresponding to different distances away (e.g., the object gets largeras it gets closer and more sensors receive more EM radiation from theobject as it gets larger). The elimination of objects allows theguidance system to zero in on the target object via the process ofelimination and also reduces computational burden by only analyzingreceived EM radiation from the remaining objects that are flagged aslikely being the target object.

Method 700 continues with block 710 where at least the objectidentification operation of block 706 and object elimination operationof block 708 are repeated using different columns of sensors associatedwith a closer distance to the areobody. The various columns of sensorsreceive light from different distances along the FOV of the areobody anda given object will be imaged across the columns of sensors of thesensor array as the areobody flies closer to it due to the push broomeffect (as discussed in more detail with reference to FIG. 1.) Accordingto some embodiments, block 704 is also repeated across sensorsassociated with different distances to perform contrast analysis andeliminate objects that are of a different size (or shape) compared tothe target object. Once all identified objects (or at least a thresholdpercentage of objects) other than the target object have beeneliminated, the guidance system on board the areobody can guide theareobody towards the target object using only contrast analysis, forexample, for the final portion of the flight to hone in on the targetobject.

Some of the embodiments discussed herein may be implemented, forexample, using a machine readable medium or article which may store aninstruction or a set of instructions that, if executed by a machine, maycause the machine to perform a method and/or operations in accordancewith the embodiments. Such a machine may include, for example, anysuitable processing platform, computing platform, computing device,processing device, computing system, processing system, computer,process, or the like, and may be implemented using any suitablecombination of hardware and/or software. The machine readable medium orarticle may include, for example, any suitable type of memory unit,memory device, memory article, memory medium, storage device, storagearticle, storage medium, and/or storage unit, such as memory, removableor non-removable media, erasable or non-erasable media, writeable orrewriteable media, digital or analog media, hard disk, floppy disk,compact disk read only memory (CD-ROM), compact disk recordable (CD-R)memory, compact disk rewriteable (CR-RW) memory, optical disk, magneticmedia, magneto-optical media, removable memory cards or disks, varioustypes of digital versatile disk (DVD), a tape, a cassette, or the like.The instructions may include any suitable type of code, such as sourcecode, compiled code, interpreted code, executable code, static code,dynamic code, encrypted code, and the like, implemented using anysuitable high level, low level, object oriented, visual, compiled,and/or interpreted programming language.

Unless specifically stated otherwise, it may be appreciated that termssuch as “processing,” “computing,” “calculating,” “determining,” or thelike refer to the action and/or process of a computer or computingsystem, or similar electronic computing device, that manipulates and/ortransforms data represented as physical quantities (for example,electronic) within the registers and/or memory units of the computersystem into other data similarly represented as physical quantitieswithin the registers, memory units, or other such information storagetransmission or displays of the computer system. The embodiments are notlimited in this context.

FURTHER EXAMPLE EMBODIMENTS

The following examples pertain to further embodiments, from whichnumerous permutations and configurations will be apparent.

Example 1 is a ground imaging system that is designed for use on aguided areobody. The ground imaging system includes one or more lensesconfigured to receive electromagnetic radiation from objects and terrainat a ground level, a filter substrate comprising a plurality of filters,a sensor array configured to receive the electromagnetic radiation fromthe filter substrate, and a processing device coupled to the sensorarray. The filter substrate is located at a focal plane of the one ormore lenses such that the filter substrate receives the electromagneticradiation from the one or more lenses. The plurality of filters includespolarization filters and multispectral filters. The processing device isconfigured to analyze multispectral and polarization signatures of theelectromagnetic radiation from the objects and terrain at the groundlevel, and determine that one or more objects is not a desired targetbased at least on the multispectral and polarization signatures of theone or more objects.

Example 2 includes the subject matter of Example 1, wherein theprocessing device comprises a field programmable gate array (FPGA).

Example 3 includes the subject matter of Example 1 or 2, wherein thepolarization filters and the multispectral filters are arranged incolumns.

Example 4 includes the subject matter of Example 3, wherein the filtersubstrate includes a first region having a first column of polarizationfilters and a first column of multispectral filters, the first column ofpolarization filters and the first column of multispectral filterscorresponding to a first column of sensors and a second column ofsensors, respectively, of the sensor array, and the filter substrateincludes a second region having a second column of polarization filtersand a second column of multispectral filters, the second column ofpolarization filters and the second column of multispectral filterscorresponding to a third column of sensors and a fourth column ofsensors, respectively, of the sensor array.

Example 5 includes the subject matter of Example 4, wherein the firstcolumn of sensors and the second column of sensors are included in afirst sensor column group, the third column of sensors and the fourthcolumn of sensors are included in a second sensor column group, thefirst sensor column group being larger than the second sensor columngroup.

Example 6 includes the subject matter of Example 4 or 5, wherein thefirst region of the filter substrate corresponds to electromagneticradiation received from objects and terrain at a first distance from theaerobody and the second region of the filter substrate corresponds toelectromagnetic radiation received from objects and terrain at a seconddistance from the aerobody, the second distance being larger than thefirst distance.

Example 7 includes the subject mater of Example 6, whereinelectromagnetic radiation received from a given object through the firstregion corresponds to first expected pixel size for the given object,and wherein electromagnetic radiation received from the given objectthrough the second region corresponds to second expected pixel size forthe given object, the first expected pixel size being larger than thesecond expected pixel size.

Example 8 includes the subject matter of Example 3, wherein each columnof the polarization filters is mapped to corresponding first columns ofsensors of the sensor array and each column of multispectral filters ismapped to corresponding second columns of sensors of the sensor array.

Example 9 includes the subject matter of Example 8, wherein thirdcolumns of sensors of the sensor array receive unfilteredelectromagnetic radiation from the filter substrate.

Example 10 includes the subject matter of Example 9, wherein theprocessing device is further configured to analyze contrast signaturesof the unfiltered electromagnetic radiation.

Example 11 includes the subject matter of Example 9 or 10, wherein thefirst columns of sensors, the second columns of sensors, and the thirdcolumns of sensors are adjacently arranged one after the other.

Example 12 includes the subject matter of any one of Examples 1-11,wherein the multispectral filters comprise a plurality of notch filters.

Example 13 includes the subject matter of any one of Examples 1-12,wherein the polarization filters comprise thin film linear polarizers.

Example 14 includes the subject matter of any one of Examples 1-13,further comprising an actuator coupled to the filter substrate andconfigured to move the filter substrate with respect to the sensorarray.

Example 15 includes the subject matter of any one of Examples 1-14,wherein the sensor array comprises a microbolometer or a focal planearray.

Example 16 is a filter substrate for use in an imaging system. Thefilter substrate is designed to receive electromagnetic radiation andmap the electromagnetic radiation onto a sensor array. The filtersubstrate includes a substrate, a plurality of polarization filtersarranged in first columns on the substrate, a plurality of multispectralfilters arranged in second columns on the substrate, and a plurality ofunfiltered regions arranged in third columns on the substrate. The firstcolumns, second columns, and third columns are adjacently arranged oneafter the other on the substrate.

Example 17 includes the subject matter of Example 16, wherein the filtersubstrate includes a first region having first, second, and thirdcolumns of a first width and a second region having first, second, andthird columns of a second width greater than the first width.

Example 18 includes the subject matter of Example 17, wherein the firstregion of the filter substrate corresponds to electromagnetic radiationreceived from a first distance from the filter substrate and the secondregion of the filter substrate corresponds to electromagnetic radiationreceived from a second distance from the filter substrate, the firstdistance being larger than the second distance.

Example 19 includes the subject matter of Example 17 or 18, wherein thefirst region of the filter substrate corresponds to imaged objectshaving a first pixel size and the second region of the filter substratecorresponds to imaged objects having a second pixel size larger than thefirst pixel size.

Example 20 includes the subject matter of any one of Examples 17-19,further comprising an unfiltered region between the first region and thesecond region having a width that spans a distance between the firstregion and the second region.

Example 21 includes the subject matter of any one of Examples 16-20,wherein the substrate comprises borosilicate glass.

Example 22 includes the subject matter of any one of Examples 16-21,wherein the plurality of multispectral filters comprise a plurality ofnotch filters.

Example 23 includes the subject matter of any one of Examples 16-22,wherein the plurality of polarization filters comprise thin film linearpolarizers.

Numerous specific details have been set forth herein to provide athorough understanding of the embodiments. It will be understood by anordinarily-skilled artisan, however, that the embodiments may bepracticed without these specific details. In other instances, well knownoperations, components and circuits have not been described in detail soas not to obscure the embodiments. It can be appreciated that thespecific structural and functional details disclosed herein may berepresentative and do not necessarily limit the scope of theembodiments. In addition, although the subject matter has been describedin language specific to structural features and/or methodological acts,it is to be understood that the subject matter defined in the appendedclaims is not necessarily limited to the specific features or actsdescribed herein. Rather, the specific features and acts describedherein are disclosed as example forms of implementing the claims.

What is claimed is:
 1. A ground imaging system configured for use on aguided aerobody, the ground imaging system comprising: one or morelenses configured to receive electromagnetic radiation from objects andterrain at a ground level; a filter substrate comprising a plurality offilters, the filter substrate located at a focal plane of the one ormore lenses such that the filter substrate receives the electromagneticradiation from the one or more lenses, wherein the plurality of filtersincludes polarization filters and multispectral filters; a sensor arrayconfigured to receive the electromagnetic radiation from the filtersubstrate; and a processing device coupled to the sensor array andconfigured to analyze multispectral and polarization signatures of theelectromagnetic radiation from the objects and terrain at the groundlevel, and determine that one or more objects is not a desired targetbased at least on the multispectral and polarization signatures of theone or more objects.
 2. The ground imaging system of claim 1, whereinthe processing device comprises a field programmable gate array (FPGA).3. The ground imaging system of claim 1, wherein the polarizationfilters and the multispectral filters are arranged in columns.
 4. Theground imaging system of claim 3, wherein the filter substrate includesa first region having a first column of polarization filters and a firstcolumn of multispectral filters, the first column of polarizationfilters and the first column of multispectral filters corresponding to afirst column of sensors and a second column of sensors, respectively, ofthe sensor array, and the filter substrate includes a second regionhaving a second column of polarization filters and a second column ofmultispectral filters, the second column of polarization filters and thesecond column of multispectral filters corresponding to a third columnof sensors and a fourth column of sensors, respectively, of the sensorarray.
 5. The ground imaging system of claim 4, wherein the first columnof sensors and the second column of sensors are included in a firstsensor column group, the third column of sensors and the fourth columnof sensors are included in a second sensor column group, the firstsensor column group being larger than the second sensor column group. 6.The ground imaging system of claim 4, wherein the first region of thefilter substrate corresponds to electromagnetic radiation received fromobjects and terrain at a first distance from the aerobody and the secondregion of the filter substrate corresponds to electromagnetic radiationreceived from objects and terrain at a second distance from theaerobody, the second distance being larger than the first distance. 7.The ground imaging system of claim 6, wherein electromagnetic radiationreceived from a given object through the first region corresponds tofirst expected pixel size for the given object, and whereinelectromagnetic radiation received from the given object through thesecond region corresponds to second expected pixel size for the givenobject, the first expected pixel size being larger than the secondexpected pixel size.
 8. The ground imaging system of claim 3, whereineach column of the polarization filters is mapped to corresponding firstcolumns of sensors of the sensor array and each column of multispectralfilters is mapped to corresponding second columns of sensors of thesensor array.
 9. The ground imaging system of claim 8, wherein thirdcolumns of sensors of the sensor array receive unfilteredelectromagnetic radiation from the filter substrate.
 10. The groundimaging system of claim 9, wherein the processing device is furtherconfigured to analyze contrast signatures of the unfilteredelectromagnetic radiation.
 11. The ground imaging system of claim 9,wherein the first columns of sensors, the second columns of sensors, andthe third columns of sensors are adjacently arranged one after theother.
 12. The ground imaging system of claim 1, wherein themultispectral filters comprise a plurality of notch filters and thepolarization filters comprise thin film linear polarizers.
 13. Theground imaging system of claim 1, further comprising an actuator coupledto the filter substrate and configured to move the filter substrate withrespect to the sensor array.
 14. The ground imaging system of claim 1,wherein the sensor array comprises a microbolometer or a focal planearray.
 15. A filter substrate for use in an imaging system, the filtersubstrate configured to receive electromagnetic radiation and map theelectromagnetic radiation onto a sensor array, the filter substratecomprising: a substrate; a plurality of polarization filters arranged infirst columns on the substrate; a plurality of multispectral filtersarranged in second columns on the substrate; and a plurality ofunfiltered regions arranged in third columns on the substrate; whereinthe first columns, second columns, and third columns are adjacentlyarranged one after the other on the substrate.
 16. The filter substrateof claim 15, wherein the filter substrate includes a first region havingfirst, second, and third columns of a first width and a second regionhaving first, second, and third columns of a second width greater thanthe first width.
 17. The filter substrate of claim 16, wherein the firstregion of the filter substrate corresponds to electromagnetic radiationreceived from a first distance from the filter substrate and the secondregion of the filter substrate corresponds to electromagnetic radiationreceived from a second distance from the filter substrate, the firstdistance being larger than the second distance.
 18. The filter substrateof claim 16, wherein the first region of the filter substratecorresponds to imaged objects having a first pixel size and the secondregion of the filter substrate corresponds to imaged objects having asecond pixel size larger than the first pixel size.
 19. The filtersubstrate of claim 16, further comprising an unfiltered region betweenthe first region and the second region having a width that spans adistance between the first region and the second region.
 20. The filtersubstrate of claim 15, wherein the plurality of multispectral filterscomprise a plurality of notch filters and the plurality of polarizationfilters comprise thin film linear polarizers.